In order to obtain high yields in production of semiconductors, it is important to take measures by finding defects that are generated in production steps at an early stage. In recent years, defects that have influence on yields have come in a variety of types with a reduction in the size of semiconductors, and the number of production steps that should be observed has also increased. For example, there have been increased cases where a production step in which image drift is generated due to electrostatic charge on a sample is subjected to defect observation.
A SEM (Scanning Electron Microscope) defect observation apparatus is an apparatus for observing such a variety of types of defects, and is typically an apparatus for observing an image of a defect position, which has been detected with an upstream defect inspection apparatus, with higher image quality than that of the upstream defect inspection apparatus. Specifically, a sample stage is moved to defect coordinates output from the upstream defect inspection apparatus, and then, an image is captured at a low magnification at about a level that allows the field of view to contain the target defect to be observed. Then, the correct defect position is identified, and the sample stage is moved so that the defect position is located at the center of the field of view or the center of image capturing is moved, and then, an image to be observed is acquired at a high magnification that is suitable for defect observation. As described above, a defect position is identified with a low-magnification image because defect coordinates output from the upstream defect inspection apparatus contain errors within the range of the specifications of the apparatus. Thus, when a high-quality defect image is acquired with a SEM defect observation apparatus, a process of correcting such errors should be performed. ADR (Automatic Defect Review or Redetection) is a technique of automating a step of acquiring a high-quality defect image.
In ADR, the conditions to acquire a low-magnification image, the conditions to acquire a high-magnification image, and the like should be optimized in accordance with the defect coordinate detection accuracy of the upstream defect inspection apparatus and the properties of a sample in order to obtain both a high defect detection rate of ADR and high throughput of ADR including the image acquisition time. However, the defect detection rate and the throughput of ADR are typically in trade-off relationship, and thus, determining optimal conditions is difficult work even for a person with experience and expertise. Therefore, it is desired to simplify the operation of setting optimal conditions.
Meanwhile, ADC (Automatic Defect Classification), which is a technique of automating a step of classifying defects by type on the basis of a defect image acquired with high quality, has also been put into practical use. In particular, the range of steps to which ADC is applied in production lines is expanding. In ADC, the defect classification accuracy rate of ADC and the throughput of ADC including the image acquisition time are also in trade-off relationship, and thus, determining optimal conditions is difficult work. Therefore, it is desired to simplify the operation of setting optimal conditions.
Patent Literature 1 discloses a technique of, with a scanning electron microscope, acquiring a plurality of frame images, which have been obtained by scanning the observation field of view, calculating the drift amount between the frame images, and overlaying the frame images with one another while correcting the drift amount, thereby obtaining a clear image even when image drift is generated.